There has been a continuing effort to replace metal components with lighter weight plastic components especially in motor vehicles and aircraft to reduce fuel consumption.
Glass fiber reinforced resin composites are being used for this purpose. These composites usually contain a binder to improve the interface, i.e. form a bond, between the glass fibers and the resin. The binder is typically applied as a size coating to the glass fibers. Conventionally, silane or titanate coupling agents are used for such size coating and they provide bonding by means of Si-O-Si and Si-O-Ti linkages. These linkages are thermally stable but on exposure to water, e.g. moisture and/or humidity, can hydrolyze and do not reform thereby causing loss of bonding to the reinforcement. Similarly cyclic stress, i.e. tensile stress caused by intermittent application of a load, e.g. during a revolution of the component, can cause a loss of this type of bonding. Even if an occurrence of exposure to moisture and/or humidity and/or cyclic stress does not cause failure, each exposure normally causes irreversible damage, and there is a cumulative effect. Thus, heretofore, composite material has not ordinarily replaced steel and other metals in parts, e.g. wheels for automobiles, normally encountering substantial exposure to moisture and/or humidity and/or cyclic stress.
McCombs et al. U.S. Pat. No. 4,318,960 discloses glass fiber reinforced plastics containing glass fibers with a size coating of maleic anhydride adduct of polybutadiene used in combination with organosilicon coupling agents. The adduct is formed in a free radical reaction in the presence of a free radical initiator. The presence of the free radical initiator produces insoluble adduct. It is therefore applied to the glass fibers from an emulsion whereby the distribution of the sizing agent normally lacks uniformity. Furthermore, it is applied in an amount to deposit a coating of 0.1 to 15% by weight. McCombs et al. does not disclose that its glass fiber reinforced plastics resist strength loss on exposure to moisture and/or humidity and/or cyclic stress.